The described invention relates in general to sharpening devices, and more specifically to a sharpener for use with pencils or other items, wherein the sharpener includes an integrated pencil-centering mechanism and optional pencil diameter selection dial. This invention also relates to an electric pencil sharpener having a tool-less cutter-carrier replacement feature that uses only one electrical switch for both pencil insertion activation and electrical interlock when the cutter-carrier is accessed for replacement. Certain aspects of this invention may be used with mechanical (i.e., crank sharpeners) and/or electric sharpeners that are consumer products or that are intended for commercial or industrial applications.
Pencils are commonly used writing or marking implements that must be regularly sharpened during use. One of the most frequent user complaints with regard to pencil sharpeners is that the pencil core is not sharpened evenly, with the graphite core being centered in the body of the sharpened pencil. A contributing factor to this problem is that the user of the pencil does not insert the pencil into the sharpener directly on axis with the internal cone of the cutter-carrier assembly of the sharpener. This may occur if the pencil is not supported radially where it enters the cutter-carrier, either due to too large an aperture (in mechanical or electric pencil sharpeners) or in some cases, in electric pencil sharpeners, due to a pencil switch actuation slide or lever that biases the pencil to one side. Commercially available electric pencil sharpeners typically include only one slide or lever which biases the pencil radially to one side and tends to push it off the axis of the cutter-carrier. Some known designs attempt to negate this effect by using two opposing slides or levers. One slide or lever actuates an electric switch while the other counteracts the switch force from the other side of the pencil. This two-slide design is an improvement, but the pencil is sometimes provided with minimal support perpendicular to the slides or levers and the self-centering tendency is often weak because the slides are mechanically independent (i.e., unlinked) and the centering effect is due to the difference between the two spring forces driving the slides or levers. Thus, there is an ongoing need for a sharpener with an effective centering mechanism.
Commercially available pencil sharpeners also typically include a simple rotating disc with a plurality of apertures having different diameters for supporting pencils of various sizes and/or shapes. This disc is positioned on an axis offset by some distance from the pencil entry aperture of the cutter-carrier with the apertures typically positioned on a circle with a radius equal to that distance so that the holes are concentric with the sharpener's cutter-carrier. With offset rotating aperture pencil-size-selection discs that are common in electric pencil sharpeners, when presented on the outside of the sharpener, with all possible pencil apertures visible, there is some ambiguity about which aperture leads to the cutter-carrier (sharpening) mechanism. In some cases, it is the aperture directly above (behind) the center axis of the dial, and in other cases, it is the aperture directly below (in front of) the dial axis. In some electric pencil sharpeners, the rotating selector dial is recessed internally within the enclosure of the sharpener, leaving only the outer circumference portion accessible for adjustment, then presenting only one pencil-entry aperture on the external enclosure. However, this makes it more difficult for the user to select the correct aperture because not all of the choices are visible at once and the direction of increasing or decreasing size is unclear. Thus, there is an ongoing need for a sharpener with an easy to understand and effective size indicator and size limiting dial.
Because the helical cutters used in electric pencil sharpeners are the primary wearing component, it is useful to provide a convenient (quick and tool-free) means of replacement when these parts eventually wear out. This can be accomplished by providing a removable cap or cover that allows user access to a removable cutter-carrier assembly. However, care must be taken so that the cutter(s) and the motor driving the cutter(s) cannot be activated while the cap or cover, which normally provides mechanical shielding from the rotating cutter(s), is removed. Such protection is commonly provided in electrical equipment by an interlock switch. It is the best practice in the industry to implement these types of interlock switches with mechanical guarding so that the switches cannot be intentionally or inadvertently reactivated (bypassed) by a finger. In existing electric pencil sharpeners that have removable covers for accessing the cutter-carrier assembly for replacement, there are usually two mechanical linkages and two electrical switches that provide for motor activation on pencil insertion and safety interlock when the cover portion is removed. Further, in electric pencil sharpeners, the motor-actuation pencil switch is commonly located on the main structure of the sharpener, adjacent to the cutter-carrier assembly. The temporary removal of the cap or cover often provides the most direct access to the cutter-carrier assembly. The cap or cover, containing the pencil-contacting portions of the switch, is then removed while the electrical and drive motor components remain with the base portion of the sharpener. The cover may contain an electrical switch and remain tethered by wires to the base sharpener, but this creates design and electrical insulation complications. Thus, there is an ongoing need for a pencil-switch-to-sharpener-base linkage that can be readily disconnected and reconnected and that provides enhanced safety.